When a silver halide color photographic material is imagewise exposed and subjected to color development, dye-forming couplers react with an oxidized aromatic primary amine developing agent to form color images. In general, in the photographic process, a color reproduction process by a subtractive color photographic process is used and for reproducing blue, green, and red images, yellow, magenta and cyan color images which are in the complementary color relation with the foregoing colors, respectively, are formed.
In this case, for the formation of cyan color images, phenol derivatives or naphthol derivatives are mainly used as the couplers. In a color photographic process, a color-forming coupler is added in a developer or is incorporated in a photosensitive photographic silver halide emulsion layer or other color image-forming layer, and by reacting with the oxidation product of a color developing agent formed by a development, a nondiffusible dye is formed.
The reaction of the coupler and the oxidized color developing agent occurs at an active site on the coupler (usually referred to as the coupling position) and the coupler having a hydrogen atom at the active site is a 4-equivalent coupler, that is, a coupler which stoichiometrically requires 4 moles of silver halide having development centers for forming 1 mole of dye. On the other hand, a coupler having at the active site a group capable of being released as an anion is a 2-equivalent coupler, that is, a coupler which requires only 2 moles of silver halide having development centers for forming 1 mole of dye. Accordingly, in the case of using the 2-equivalent coupler, the amount of silver halide in a silver halide emulsion layer can generally be reduced, and hence the layer thickness can be reduced as compared to the case of using the 4-equivalent coupler, whereby the processing time for the photographic material can be shortened, and the sharpness of the color images is improved.
Typical examples of such releasable groups include a sulfonamide group as described in U.S. Pat. No. 3,737,316; an amido group as described in U.S. Pat. No. 3,749,735; a sulfonyl group as described in U.S. Pat. No. 3,622,238; an aryloxy group as described in U.S. Pat. No. 3,476,563; an acyloxy group as described in U.S. Pat. No. 3,311,476; a thiocyano group as described in U.S. Pat. No. 3,214,437; an isothiocyanate group as described in U.S. Pat. No. 4,032,345; a sulfonyloxy group as described in U.S. Pat. No. 4,046,573; an alkylthio group as described in U.S. Pat. No. 3,227,554; a thiocarbonyloxy group as described in Japanese Patent Application (OPI) No. 51939/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"); an aralkenylcarbonyloxy group as described in Japanese Patent Publication No. 46059/82; an acylamino group as described in Japanese Patent Application (OPI) No. 21828/76; an aminomethyl group as described in Japanese Patent Application (OPI) No. 52828/76 and Japanese Patent Publication No. 6537/81; heterocyclic oxy groups as described in Japanese Patent Application (OPI) Nos. 37425/72 and 200039/82; and substituted alkoxy groups as described in U.S. Pat. No. 3,227,551, Japanese Patent Application (OPI) Nos. 90932/77, 99938/78, 105226/78, 14736/79, 66129/79, 32071/80, 65957/80, 1938/81, 6593/81, 12643/81, 27147/81 and 80044/81 and Japanese Patent Publication Nos. 120334/75, 37822/79, 6539/81, 3934/82 and 46060/82.
Furthermore, by properly selecting the releasable group of a coupler, it is possible to incorporate, for example, a diffusible dye moiety in the releasable group and apply the coupler to a diffusion transfer photographic system of forming dye images of diffusible dye in an image-receiving layer by utilizing the releasing dye. Couplers of this type are called "diffusible dye-releasing couplers" and they are described, for example, in U.S. Pat. Nos. 3,227,550 and 3,765,886, U.S. Defensive Publication T900,029, British Pat. No. 1,330,524, etc.
Also, certain kinds of colored 2-equivalent couplers have a masking effect for color correcting dye images. These couplers are called "colored couplers" and are described, for example, in Japanese Patent Application (OPI) No. 26034/76.
A 2-equivalent coupler having a releasable product which has the effect of inhibiting development is called a "development inhibitor-releasing coupler", and since the coupler inhibits the development in proportion to the amount of developed silver, the coupler has the effects of fining image grains, controlling gradation of images, improving the color reproducibility, etc. Also, the coupler can be utilized for a diffusion transfer system by utilizing the action to the adjacent layer. Such couplers are described, for example, in U.S. Pat. No. 3,227,554, Japanese Patent Application (OPI) No. 122335/74, West German Patent Application (OLS) No. 2,414,006, etc.
Since 2-equivalent couplers essentially have several excellent advantages as compared with 4-equivalent couplers as described above, 2-equivalent couplers tend to be frequently used.
On the other hand, phenol series cyan couplers having a ureido group at the 2-position and an acylamino group at the 5-position are said to form color images excellent in fastness to heat or light by color development as compared to other phenol series cyan couplers or naphthol series couplers and these cyan couplers are described, for example, in Japanese Patent Application (OPI) Nos. 65134/81, 204543/82, 204554/82, 204545/82, 33249/83, 33250/83, 33251/83, 33252/83, etc. These cyan couplers include 2-equivalent couplers.
However, conventional phenol series 2-equivalent cyan couplers having a ureido group at the 2-position and an acylamino group at the 5-position have some disadvantages in that their coupling reactivity is insufficient, they have a significant color fog problem, they have poor dispersibility thus cause coating problems, and such couplers are unstable and hence cannot be stored for a long period of time without degradation. Also, the stability of the color images formed by color development by heat or light is still insufficient in the case of storing the color images for a long period of time.